Noninvasive sensor housing

ABSTRACT

A flexible sensor pad includes a cavity to hold a sensor unit with an attached cable. According to one aspect of the present invention, a light-shielding layer is coupled to a bottom surface of the sensor pad, surrounds the sensor unit, and extends past two sides of the sensor pad. A transparent adhesive layer is coupled to the light-shielding layer and extends past two sides of the light-shielding layer. Another light shielding layer is coupled to a top surface of the sensor pad and covers the sensor unit. The cable divides the sensor pad into a first side and a second side which are mirror images of each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. design patentapplications 29/281,486, filed Jun. 25, 2007, issued as U.S. design Pat.No. D567,949 on Apr. 29, 2008, and 29/303,969, filed Feb. 21, 2008,which are incorporated by reference along with all other referencescited in this application.

BACKGROUND OF THE INVENTION

The present invention relates to medical devices and their manufacture.More particularly, the present invention relates to patient monitoringdevices and methods.

Patient monitoring systems measure, display, and sometimes storephysiological data. Patient monitoring systems are now used in a widevariety of applications. This includes, for example, hospital,ambulatory, and home health care. Hospitals routinely measure andanalyze the vital signs of surgical, trauma, and other patients fromadmission through discharge. There are many different types ofmonitoring devices. For example, there are monitoring devices for bloodpressure, body temperature, heart activity, blood gases, cholesterol,glucose, pulse rate, respiration rate, tissue oxygen saturation, andmany other parameters.

Noninvasive monitoring devices fulfill an important role in assessing,tracking, diagnosing, and treating patients. These devices enable earlydiagnosis, treatment of acute conditions, and reduce the need forinvasive interventions. Some types of monitoring devices gather patientdata via sensors attached to the patient.

In order for the sensors gather accurate information, it is importantthat they are protected from outside interference. They should also becomfortable for the patient to wear as the sensors may be attached tothe patient for long periods of time. Furthermore, anything that touchesor comes near the patient must be sterile. Thus, sterility is also aconcern. These are just a few examples of desirable features.

There is, then, a continuing demand for medical devices that are easierto use, safer to use, usable in locations outside the hospital, providemore features, and generally address the needs of patients, doctors,nurses, clinicians, first responders, and others in the medicalcommunity.

Therefore, there is a need to provide improved systems and techniquesfor monitoring patients.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to patient monitoring devices. In anembodiment, the invention is a device that includes a pad region with acavity, a first light-shielding layer, coupled to the pad region, wherethe first light-shielding layer has an opening that overlaps with atleast a portion of the cavity, and an adhesive layer, coupled to thefirst light-shielding layer, where the adhesive layer extends past atleast one edge of the first light-shielding layer.

The device may further include a sensor unit positioned in the cavityand a cable coupled to the sensor unit, where the cable is arranged toenter the cavity, the cable being arranged to define a longitudinal axisthat passes through the cable and the device, dividing the device into afirst side and a second side, where the first and second sides aremirror images of each other. The cable may have a length greater than1.2 meters. The bottom surface area of the pad region may be greaterthan a bottom surface area of a sensor unit recessed into the cavity.

In an embodiment, the pad region, first light-shielding layer, andadhesive layer each include at least two opposing straight edges whichare parallel, the pad region, first light-shielding layer, and adhesivelayer being arranged so that the at least two opposing straight edges ofthe pad region, first light-shielding layer, and adhesive layer overlap,the adhesive layer further includes a left portion having a shape of asemicircle, a middle portion having a shape of a polygon, and a rightportion having a shape of a semicircle, where the middle portion isbetween the left portion and the right portion.

The thickness of the pad region when uncompressed may be thicker than asensor unit. A stiffener bar may be coupled to a top surface of the padregion, above at least a portion of the cavity. The device may furtherinclude a release liner, coupled to the adhesive layer, where therelease liner includes a tab positioned along an edge where a cableenters the pad region. The adhesive layer may be transparent.

In an embodiment, the sensor unit includes a first source structure, asecond source structure, a first detector structure include opticalfiber, and a second detector structure including optical fiber. A firstdistance is between the first source structure and the first detectorstructure, a second distance is between the first source structure andthe second detector structure, a third distance is between the secondsource structure and the first detector structure, a fourth distance isbetween the second source structure and the second detector structure.The first distance is not equal to the second, third, and fourthdistances, the second distance is not equal to the third and fourthdistances, and the third distance is not equal to the fourth distance.

In an embodiment, the device may further include a secondlight-shielding layer coupled to a top surface of the pad region, wherethe second light-shielding layer has an opening that overlaps with atleast a portion of the cavity. A ratio of a thickness of the pad regionto a length of the adhesive layer may be less than 0.1. The pad regionmay have a thickness at least about 3.2 millimeters. An edge of thecavity may overlap with an edge of the pad region.

In an embodiment, the device may further include a third light-shieldinglayer, where the third light-shielding layer includes a coupled portionand an uncoupled portion, where the coupled portion is coupled to thedevice and does not overlap the cavity, and the uncoupled portionoverlaps the cavity.

In an embodiment, the invention is a device including a pad region witha cavity, a first light-shielding layer, coupled to the pad region, andan adhesive layer, coupled to the first light-shielding layer. Aperipheral outline forms an outer boundary of the adhesive layer, andall points on a line drawn between any point on the peripheral outlineto any other point on the peripheral outline are enclosed by the outerboundary.

The adhesive layer may further include a first convex edge, a secondconvex edge, a first straight edge, and a second straight edge. Thefirst straight edge may be parallel to the second straight edge, thefirst and second straight edges may be between the first and secondconvex edges, and the first convex edge may be a mirror image of thesecond convex edge.

The device may further include a sensor unit positioned in the cavity,and a cable coupled to the sensor unit, where the cable has a lengthgreater than 1.2 meters. Furthermore, the adhesive layer may betransparent.

In an embodiment, the invention is a device including a sensor unit,where the sensor unit includes a first source structure, a second sourcestructure, a first detector structure, and a second detector structure.A cable is coupled to the sensor unit. The invention may further includea sensor pad, coupled to the sensor unit. The sensor pad includes alight-shielding layer coupled to a bottom surface of the sensor pad andextending beyond a first and second edge of the sensor pad in at leasttwo opposite directions. An adhesive layer may be coupled to thelight-shielding layer and extend beyond a first and second edge of thelight-shielding layer in at least two opposite directions.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an oximeter system for measuring oxygen saturation of bloodin a patient.

FIG. 2 shows in greater detail, a block diagram of a specificimplementation of the system in FIG. 1.

FIG. 3 shows an oximeter system that includes a console, cable, sensorunit and sensor housing in accordance with an embodiment of the presentinvention.

FIG. 4 shows the wireless transfer of patient data from a field locationto a receiving location.

FIG. 5 shows a top side of a sensor housing in accordance with anembodiment of the present invention.

FIG. 6 shows an adhesive layer in accordance with an embodiment of thepresent invention.

FIG. 7 shows a bottom side of a sensor housing in accordance with anembodiment of the present invention.

FIG. 8 shows a sensor unit with a pair of light sources that are in anoffset arrangement relative to a set of four detectors in accordancewith a first embodiment of the present invention.

FIG. 9 shows a sensor unit with a pair of light sources that are in anoffset arrangement relative to a set of four detectors in accordancewith a second embodiment of the present invention.

FIG. 10 shows a cross-sectional view of a sensor housing where a cavityin a cushioning layer for a cable is located between the top and bottomsurfaces of a cavity for a sensor unit in accordance with a firstembodiment of the present invention.

FIG. 11 shows a cross-sectional view of a sensor housing where cavitiesfor a cable and a sensor unit have the same thickness as a cushioninglayer for the sensor unit in accordance with a second embodiment of thepresent invention.

FIG. 12 shows a cross-sectional view of a sensor housing where cavitiesin a cushioning layer for a sensor unit and a cable have the same depthin accordance with a third embodiment of the present invention.

FIG. 13 shows a cross-sectional view of a sensor housing where topsurfaces of cavities for a sensor unit and a cable are on the same planein accordance with a fourth embodiment of the present invention.

FIG. 14 shows a cross-sectional view of a sensor housing where bottomsurfaces of cavities for a sensor unit and a cable are on the same planein accordance with a fifth embodiment of the present invention.

FIG. 15 shows a sensor housing placed on a patient's palm in accordancewith a first embodiment of the present invention

FIG. 16 shows a process flow of using a sensor housing in accordancewith a first embodiment of the present invention.

FIG. 17 shows a sensor unit placed on a patient's fingertip inaccordance with a second embodiment of the present invention.

FIG. 18 shows a process flow of a sensor unit without the sensor housingin accordance with a second embodiment of the present invention.

FIG. 19 shows a process flow for manufacturing a sensor housing inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an oximeter system 101 for measuring oxygen saturation ofblood in a patient. The system includes a system unit 105 and a sensorprobe 108, which is connected to the system unit via a wired connection112. Connection 112 may be an electrical, optical, or another wiredconnection including any number of wires (e.g., one, two, three, four,five, six, or more wires or optical fibers). In other implementations ofthe invention, however, connection 112 may be wireless such as via aradio frequency (RF) or infrared communication.

Typically, the system is used by placing the sensor probe in contact orclose proximity to tissue (e.g., skin) at a site where an oxygensaturation or other related measurement is desired. The system unitcauses an input signal to be emitted by the sensor probe into the tissue(e.g., human tissue). There may be multiple input signals, and thesesignals may have varying or different wavelengths. The input signal istransmitted into or through the tissue.

Then, after transmission through or reflection off the tissue, thesignal is received at the sensor probe. This received signal is receivedand analyzed by the system unit. Based on the received signal, thesystem unit determines the oxygen saturation of the tissue and displaysa value on a display of the system unit.

In an implementation, the system is a tissue oximeter, which can measureoxygen saturation without requiring a pulse or heart beat. A tissueoximeter of the invention is applicable to many areas of medicine andsurgery including plastic surgery and spinal surgery, and patientmonitoring such as during patient transport. Applications may alsoinclude use with intensive care patients, nursing home patients, andpatients with acute illnesses. The tissue oximeter can make oxygensaturation measurements of tissue where there is no blood flow or pulse;such tissue, for example, may have been separated from the body (e.g., aflap) and will be transplanted to another place in the body.

Aspects of the invention are also applicable to a pulse oximeter. Incontrast to a tissue oximeter, a pulse oximeter requires a pulse inorder to function. A pulse oximeter typically measures the absorbancesof light due to the pulsing arterial blood.

There are various implementations of systems and techniques formeasuring oxygen saturation such as discussed in U.S. Pat. Nos.6,516,209, 6,587,703, 6,597,931, 6,735,458, 6,801,648, and 7,247,142.These patents are assigned to the same assignee as this patentapplication and are incorporated by reference.

FIG. 2 shows greater detail of a specific implementation of the systemof FIG. 1. The system includes a processor 204, display 207, speaker209, signal emitter 231, signal detector 233, volatile memory 212,nonvolatile memory 215, human interface device or HID 219, I/O interface222, and network interface 226. These components are housed within asystem unit enclosure. Different implementations of the system mayinclude any number of the components described, in any combination orconfiguration, and may also include other components not shown.

The components are linked together using a bus 203, which represents thesystem bus architecture of the system. Although this figure shows onebus that connects to each component, the busing is illustrative of anyinterconnection scheme serving to link the subsystems. For example,speaker 209 could be connected to the other subsystems through a port orhave an internal direct connection to processor 204.

A sensor probe 246 of the system includes a probe 238 and connector 236.The probe is connected to the connector using wires 242 and 244. Theconnector removably connects the probe and its wires to the signalemitter and signal detectors in the system unit. There is one cable orset of cables 242 to connect to the signal emitter, and one cable or setof cables 244 to connect to the signal detector. In an implementationthe cables are fiber optic cables, but in other implementations, thecables are electrical wires.

The connector may have a locking feature; e.g., insert connector, andthen twist or screw to lock. If so, the connector is more securely heldto the system unit and it will need to be unlocked before it can beremoved. This will help prevent accidental removal of the probe.

The connector may also have a first keying feature, so that theconnector can only been inserted into a connector receptacle of thesystem unit in one or more specific orientations. This will ensure thatproper connections are made.

The connector may also have a second keying feature that provides anindication to the system unit which type probe of probe is attached. Thesystem unit may handle making measurements for a number of differenttypes of probes. The second keying feature will let the system unit knowwhich type of probe is connected, so that it can perform the rightfunctionality, use the proper algorithms, or otherwise make adjustmentsits the operation for a specific probe type.

In various implementations, the system is powered using a wall outlet orbattery powered, or both. Block 256 shows power block of the systemhaving both AC and battery power options. In an implementation, thesystem includes an AC-DC converter 253. The converter takes AC powerfrom a wall socket, converts AC power to DC power, and the DC output isconnected to the components of the system needing power (indicated by anarrow 254). In an implementation, the system is battery operated. The DCoutput of a battery 256 is connected the components of the systemneeding power (indicated by an arrow 257). The battery is rechargedusing a recharger circuit 259, which received DC power from an AC-DCconverter. The AC-DC converter and recharger circuit may be combinedinto a single circuit.

The nonvolatile memory may include mass disk drives, floppy disks,magnetic disks, optical disks, magneto-optical disks, fixed disks, harddisks, CD-ROMs, recordable CDs, DVDs, recordable DVDs (e.g., DVD-R,DVD+R, DVD-RW, DVD+RW, HD-DVD, or Blu-ray Disc), flash and othernonvolatile solid-state storage (e.g., USB flash drive),battery-backed-up volatile memory, tape storage, reader, and othersimilar media, and combinations of these.

The processor may include multiple processors or a multicore processor,which may permit parallel processing of information. Further, the systemmay also be part of a distributed environment. In a distributedenvironment, individual systems are connected to a network and areavailable to lend resources to another system in the network as needed.For example, a single system unit may be used to collect results fromnumerous sensor probes at different locations.

Aspects of the invention may include software executable code orfirmware (e.g., code stored in a read only memory or ROM chip). Thesoftware executable code or firmware may embody algorithms used inmaking oxygen saturation measurements of the tissue. The softwareexecutable code or firmware may include code to implement a userinterface by which a user uses the system, displays results on thedisplay, and selects or specifies parameters that affect the operationof the system.

Further, a computer-implemented or computer-executable version of theinvention may be embodied using, stored on, or associated with acomputer-readable medium. A computer-readable medium may include anymedium that participates in providing instructions to one or moreprocessors for execution. Such a medium may take many forms including,but not limited to, nonvolatile, volatile, and transmission media.Nonvolatile media includes, for example, flash memory, or optical ormagnetic disks. Volatile media includes static or dynamic memory, suchas cache memory or RAM. Transmission media includes coaxial cables,copper wire, fiber optic lines, and wires arranged in a bus.Transmission media can also take the form of electromagnetic, radiofrequency, acoustic, or light waves, such as those generated duringradio wave and infrared data communications.

For example, a binary, machine-executable version, of the software ofthe present invention may be stored or reside in RAM or cache memory, oron a mass storage device. Source code of the software of the presentinvention may also be stored or reside on a mass storage device (e.g.,hard disk, magnetic disk, tape, or CD-ROM). As a further example, codeof the invention may be transmitted via wires, radio waves, or through anetwork such as the Internet. Firmware may be stored in a ROM of thesystem.

Computer software products may be written in any of various suitableprogramming languages, such as C, C++, C#, Pascal, Fortran, Perl, Matlab(from MathWorks, www.mathworks.com), SAS, SPSS, JavaScript, AJAX, andJava. The computer software product may be an independent applicationwith data input and data display modules. Alternatively, the computersoftware products may be classes that may be instantiated as distributedobjects. The computer software products may also be component softwaresuch as Java Beans (from Sun Microsystems) or Enterprise Java Beans (EJBfrom Sun Microsystems).

An operating system for the system may be one of the Microsoft Windows®family of operating systems (e.g., Windows 95, 98, Me, Windows NT,Windows 2000, Windows XP, Windows XP x64 Edition, Windows Vista, WindowsCE, Windows Mobile), Linux, HP-UX, UNIX, Sun OS, Solaris, Mac OS X,Alpha OS, AIX, IRIX32, or IRIX64. Microsoft Windows is a trademark ofMicrosoft Corporation. Other operating systems may be used, includingcustom and proprietary operating systems.

Furthermore, the system may be connected to a network and may interfaceto other systems using this network. The network may be an intranet,internet, or the Internet, among others. The network may be a wirednetwork (e.g., using copper), telephone network, packet network, anoptical network (e.g., using optical fiber), or a wireless network, orany combination of these. For example, data and other information may bepassed between the computer and components (or steps) of a system of theinvention using a wireless network using a protocol such as Wi-Fi (IEEEstandards 802.11, 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, and802.11n, just to name a few examples). For example, signals from asystem may be transferred, at least in part, wirelessly to components orother systems or computers.

In an embodiment, through a Web browser or other interface executing ona computer workstation system or other device (e.g., laptop computer,smartphone, or personal digital assistant), a user accesses a system ofthe invention through a network such as the Internet. The user will beable to see the data being gathered by the machine. Access may bethrough the World Wide Web (WWW). The Web browser is used to downloadWeb pages or other content in various formats including HTML, XML, text,PDF, and postscript, and may be used to upload information to otherparts of the system. The Web browser may use uniform resourceidentifiers (URLs) to identify resources on the Web and hypertexttransfer protocol (HTTP) in transferring files on the Web.

FIG. 3 shows a system 300 incorporating a sensor housing 304 with asensor unit 308 of the invention. The system includes a monitoringconsole 312 and a cable 316. A connector 301 at an end of the cableconnects the sensor unit to the monitoring console. The cable,connector, sensor unit, and sensor housing are disposable.

The length of the cable may vary. In a specific implementation, thelength of the cable ranges from about 1.2 meters to about 3 meters. Forexample, the cable may be about 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2,2.1, 2.2, 2.3, 2.4, or 2.5 meters long or greater. Depending on thespecific application, the cable length may be less than 1.2 meters. Insome applications, the cable length will be greater than 3 meters.

A specific application of the invention is operating room use or otherplaces where it is desirable to maintain cleanliness and sterileconditions, such as isolation units. Patients in isolation units mayhave contagious diseases or compromised immune systems. Hospitals needto ensure that patients with a contagious disease do not infect others.Items introduced near the patient must either be disposed after use orproperly cleaned. Hospitals also need to protect patients withcompromised immune systems from sources of microorganisms. In thesecases, a longer cable length, such as greater than 1.2 meters, isadvantageous because this helps to separate the patient from sources ofcontamination, such as the console. Similarly, a longer cable lengthalso minimizes contamination of, for example, the console by thepatient.

The sensor housing, sensor unit, entire length of the cable, and theconnector are packaged as a probe unit in a sterile package. The probeunit is detachable from the console after use and may be disposed. Auser may then open a new sterile package containing a new probe unit.The package may be opened at the time of actual use or near the time ofactual use so as to not contaminate the probe unit. The user can thenconnect this new and sterile probe unit to the console to beginmonitoring. This disposable feature provides an additional level ofprotection in maintaining a sterile field around the patient.

Short cables may pose a problem. For example, short cables bringwhatever element they are connected to within close proximity to thepatient. Doctors and nurses must then devote additional care and time toensure a sterile field around the patient. This may include, forexample, additional cleansing of the elements before and afterintroduction to the sterile field, or sterile drapes on the elements.

In an implementation, the cable includes one or more optical wave guidesenclosed in a flexible cable jacket. The optical wave guides may havethe shape of a polygon, such as a square, rectangle, triangle, or othershape. In other cases, the optical wave guides may have circular or ovalshapes.

In a specific implementation, the optical wave guides are multiplestrands of fiber optic cable. The flexible cable jacket may bethin-walled PVC with or without an aluminum helical monocoil, shrinkwrap tubing, plastic, rubber, or vinyl. In other implementations,however, the cable is standard electrical wiring (e.g., copper oraluminum wire), which is stranded or solid core, or coaxial cable, orany combination of these.

Further, the cable may also include a combination of one or more opticalwave guides and electrical wiring. In a specific embodiment, theelectrical wiring and each optical wave guide may be enclosed in theirown separate flexible cable jacket. In another embodiment, multipleoptical wave guides may be enclosed in a flexible cable jacket, separatefrom the cable jacket enclosing the electrical wiring. In yet anotherembodiment, both the optical wave guides and electrical wiring will beenclosed in the same flexible cable jacket.

In an implementation, the cable is passive. It does not contain anyactive, generative properties to maintain signal integrity. However, inother implementations, the cable includes active components. Forexample, the cable may amplify the signal at the sensor unit.Particularly long lengths of cable subject to significant attenuationmay require amplification. Amplification may also be required if themonitored site contains a particularly dense structure such as bone.

In a specific embodiment utilizing multiple fiber optic cables, all ofthe fiber optic cables are enclosed within one end, or both ends of theflexible cable jacket. Minimizing the number of exposed cables lowersthe likelihood that the cables will get entangled. In anotherembodiment, the fiber optic cables are not enclosed together and insteadeach fiber optic cable is enclosed in its own flexible cable jacket.

In an implementation, the cable and monitoring console have indicators.The indicators may be color indicators that are painted on, or raisedindicators, or both. These indicators help the user to properly attachthe cable to the monitoring console. For example, the indicators mayinclude two green arrows placed on the cable and monitoring console,respectively. When the arrows are aligned the cable is properlyattached. Further, there may be instructions printed on the console,cable, or both that instruct the user on the proper attachment of thecable to the console.

A coupling at the end of the cable attached to the monitoring consoleprotects the cable from accidental disconnection. The coupling may be athreaded collar on a cable end that threads onto the monitoring console.Alternatively, the coupling may be a lug closure, press-fit, orsnap-fit.

In an implementation, the console is portable. Thus, the console can behand-carried or mounted to an intravenous (IV) pole. A portable consolecan follow a patient anywhere in the hospital, eliminating the need tochange connections whenever a patient is moved. Moreover, a portabledesign facilitates use and assessments in numerous other locationsbesides a hospital.

A portable console is typically battery-operated. The battery istypically a rechargeable type, such as having nickel cadmium (NiCd),nickel metal hydride (NiMH), lithium ion (Li-Ion), lithium polymer, leadacid, or another rechargeable battery chemistry. The system can operatefor a certain amount of time on a single battery charge. After thebattery is drained, it may be recharged and then used again.

The portable console may also have a power-saving feature. This reducesbattery consumption during continuous measurements. The power-savingfeature may, for example, darken the console's display screen after acertain time of inactivity. The time may be approximately five, ten,fifteen, or twenty minutes. In an embodiment, the user may program thetime.

In a specific implementation, the portable console weighs approximately4.3 kilograms. However, the weight may vary from about 3 kilograms toabout 7 kilograms including, for example, 3.5, 4, 4.5, 5, 5.5, 6, 6.5,or more than 7 kilograms. In other implementations, the weight may beless than 3 kilograms. The variation is due, in part, to the type ofbattery used in an implementation. For example, lead acid batteries aretypically heavier and less compact, but less costly than NiCd or NiMHbatteries. Thus, in an application where portability and size is a highpriority such as in the small confines of a vehicle (e.g., ambulance) alighter portable console may be used. However, where portability is alower priority, such as in a hospital room, a heavier portable consolemay be used.

In another implementation, the console is not hand-held or portable. Theconsole may be a large, nonportable device that is attached to a wall orsecured to a stand or surface. In this implementation, the system istypically connected to AC power. A battery may be used as a back-up tothe AC power.

In a specific implementation, the console provides alerts. The alertsmay be visual (e.g., a flashing light on a display of the console),audible, or both. Visual alerts may be designed so that they areviewable from any location (e.g., flashing light on the top of theconsole). In a chaotic and noisy situation, this allows users to quicklyrespond to a patient. These alerts may signal a problem with the system.This includes, for example, insufficient signal strength, kinks or sharpbends in the cable, debris on the sensor unit, debris on a couplingsurface between the cable and the console, insufficient electricalpower, a low battery, an improperly attached cable, or other problem. Analert may also signal when the system is ready for patient monitoring.The alerts may also provide warnings at certain oxygen saturationlevels. Different alerts may be used depending on the type of problemdetected by the system. Different alerts include different colors,sounds, and intensities of colors and sounds.

The console may provide an alert when the sensor unit is placed in asuitable location for a measurement. The alert may vary in intensitydepending on the suitability of the location. For example, a beepingsound may increase in frequency with more suitable locations. The alertmay be audible, visual, or both. A benefit to an audible alert is thatit allows the user to determine the suitability of a location withouthaving to look away from the patient.

The alerts may be user-programmable. That is, users may, for example,set which alerts are enabled, the threshold at which they are activated,the intensities of the alerts, and more. For example, a user may decideto enable an oxygen saturation alert, set the alert to occur if and whenthe oxygen saturation level falls below a certain value, and set thevolume level of the alert.

The console may also include a mass storage device to store data. Massstorage devices may include mass disk drives, floppy disks, magneticdisks, fixed disks, hard disks, CD-ROM and CD-RW drives, DVD-ROM andDVD-RW drives, flash and other nonvolatile solid-state storage drives,tape storage, reader, and other similar devices, and combinations ofthese.

The stored data may include patient information. This includes, forexample, the patient's name, social security number, or otheridentifying information, oxygen saturation measurements and the time anddate measured. The oxygen saturation measurements may include high, low,and average values and elapsed time between measurements.

The above drives may also be used to update software in the console. Theconsole may receive software updates via a communication network such asthe Internet.

In an implementation, the console also includes an interface fortransferring data to another device such as a computer. The interfacemay be a serial, parallel, universal serial bus (USB) port, RS-232 port,printer port, and the like. The interface may also be adapted forwireless transfer and download, such as an infrared port. The systemtransfers data without interruption in the monitoring of the patient.

A screen 320 on the console displays the patient's data. The screen maybe a flat panel display such as a liquid crystal display (LCD), plasmadisplay, thin film transistor liquid crystal display (TFT LCD),electro-luminescent (EL), or organic light emitting diode (OLED)display. The screen may include a touch screen interface. Such touchscreen interfaces are easier to clean compared to keypads if they becomecontaminated because they do not contain mechanical parts.

The screen may display numbers, text, graphics, and graphical trends incolor. Different colors may correspond to different measurements orthreshold levels. The text and numbers may be displayed in specificlanguages such as English, Spanish, French, Japanese, or Tagalog. Thedisplayed language may be user-programmable.

Users can also vary the size of the displayed information on theconsole's screen. This allows the display to be viewed at a distance,increases the viewing angle, and allows users with vision limitations tosee the information.

FIG. 4 shows an example of a wireless implementation of the invention. Asystem 400 includes a monitoring console 405 at a field location 410which transmits 415 the patient's data to a receiving location 420. Thefigure shows the monitoring console transmitting the data, using forexample, a modem in the monitoring console. However, in a differentimplementation, a sensor unit 425 may wirelessly transmit the data thereceiving location.

In the figure, the field location is in an ambulance. The ambulance istransporting a patient 430 to a hospital. In other implementations, thefield location may be in another type of vehicle such as a car,automobile, truck, bus, train, plane, boat, ship, submarine, orhelicopter. The field location may also be on a battlefield, at anaccident scene such as a car accident, at a natural disaster scene suchas an earthquake, hurricane, fire, or flood, in a patient's home, at apatient's place of work, or in a nursing home.

The receiving location also varies. The receiving location may be ahospital, clinic, trauma center, physician's home or office, or anurse's home or office. The monitoring console or sensor unit may alsotransmit to multiple receiving locations. For example, data may betransmitted to both the hospital and the physician's home.

A variety of devices may receive the data. This includes, for example, amonitoring console, other monitoring stations, mobile devices (e.g.,phones, pagers, personal digital assistants or PDAs, laptops), orcomputers, or combinations of these.

The distance between the field and receiving location may vary. Thefield and receiving location could be in different countries, states,cities, area codes, counties, zip codes. In other cases, the fieldlocation and receiving location may be in different parts of the sameroom or in different rooms in the same building.

The wireless transmission may be analog or digital. Although FIG. 4shows the system transmitting data directly to the receiving location,this is not always the case. The system may relay data to the receivinglocation using intermediaries. For example, satellites may rebroadcast atransmission. While in one embodiment, a communication network is theInternet, in other embodiments, the communication network may be anysuitable communication network including a local area network (LAN), awide area network (WAN), a wireless network, an intranet, a privatenetwork, a dedicated network, phone lines, cellular networks, a publicnetwork, a switched network, and combinations of these and the like.Wireless technologies that the system may employ include: Wi-Fi,802.11a, 802.11b, 802.11g, 802.11n, or Bluetooth, or combinations ofthese and the like. The system also has the ability to switch from onecommunication technique to another if, for example, the current networkis unreliable or there is interference. The switch may either beautomatic or manual.

The system's ability to wirelessly transmit data offers severaladvantages. It reduces the time to treatment for a patient. For example,data sent from an ambulance en route to a hospital allows a physician atthe hospital to mobilize personnel and equipment before the patient evenarrives. Another advantage is long-distance monitoring. For example,patients may use the system in their own homes. The system will then, ona continuous basis if desired, transmit data to a receiving location,such as a hospital. A nurse or physician at the hospital can then reviewthe data. If the data indicates a problem with the patient, then thehospital can dispatch an ambulance to the patient's home.

FIG. 5 shows a top side of a sensor housing 503 in accordance with animplementation. The sensor housing includes a cushioning layer 505 inwhich a sensor unit 508 is embedded. A cable 511 is coupled to thesensor unit. The cushioning layer is between a first light-shieldinglayer 514 and a second light-shielding layer 517. Though not shown inthis figure, an additional third light-shielding layer may be above thefirst light-shielding layer. An adhesive film 520 with a release linerforms the base of the sensor housing.

A stiffener bar 523 may be attached near a bottom edge 526 of the sensorhousing. In a specific embodiment, the stiffener bar may beapproximately 0.76 to 1.27 millimeters from the bottom edge of thesensor housing. It may be approximately 0.51 to 1.52 millimeters from aside edge of the cushioning layer, including 1.02 millimeters. Thestiffener bar may also be positioned on the bottom edge of the sensorhousing. In a specific embodiment, the stiffener bar is placed aboveboth the cushioning and light-shielding layers. In another embodiment,the stiffener bar is embedded within the cushioning layer, but above thecable. The common theme in all the embodiments is that the stiffener baris placed above the cable.

The stiffener bar is typically a rigid material. In a specificimplementation, the stiffener bar is polyester single coated with anadhesive film. In alternative embodiments it is made of other plasticssuch as other crystallized polymers (e.g., polypropylene orpolyethylene) or other rigid material such as metal (e.g., steel oraluminum), carbon fiber, composites, nylon, ceramics, or cardboard.

The stiffener bar is optional. Embodiments not including the bar willnot interfere with the functionality of the sensor housing. In anembodiment including the stiffener bar, the bar reduces the transmissionof cable rotational torque to the sensor unit. It also reduces themovement of the sensor unit when the cable is pulled up perpendicularlyto the patient's skin surface. The stiffener bar also helps when onetries to remove the sensor pad by pulling on the cable only. So theentire sensor pad will be lifted off instead of just having the sensorbe pulled out of the sensor pad housing.

In a specific embodiment, the cushioning layer has the shape of apolygon. It may be made of foam, specifically, ⅛″ (3.18 millimeters)thick cross-linked polyethylene foam coated on one side with amedical-grade adhesive (e.g. pressure sensitive medical-grade acrylicadhesive) with a white release liner (e.g., 92 pound, bleached kraftpaper, polycoated, silicone treated on one side), such as that made byScapa North America of Windsor, Conn. and available as part no. 0399003.In this specific embodiment, thickness of the foam is determined underAmerican Society for Testing Materials (ASTM) D1005-95.

In this specific embodiment, the adhesive properties may further includea thickness of 1.5 mils as determined under ASTM D1000-93, a value oftearing bond for adhesion to steel, and a value of tearing bond foradhesion to backing as determined under the Pressure Sensitive TapeCouncil (PSTC) test method number 1 with a 30 minute dwell time.

In other embodiments, the cushioning layer is polystyrene, paper,corrugated fiberboard, polypropylene, polyurethane, an inflated airpillow, silicon, latex, rubber, or molded pulp. The cushioning layer mayhave a 20 to 60 type A durometer.

The exact dimensions of the cushioning layer vary with the size of theembedded sensor unit. Typically, the cushioning layer, whenuncompressed, is thicker than the thickness of the sensor unit in orderto provide proper support. For example, if the thickness of the sensorunit is x, then the thickness of the uncompressed cushioning layershould be greater than x.

In an implementation, the bottom surface area of the cushioning layer isgreater than the bottom surface area of the sensor unit. For example,the bottom surface area of the cushioning layer may range fromapproximately 200 to 700 percent greater than the bottom surface area ofthe sensor unit. This includes, for example, 225, 250, 275, 300, 325,350, 375, 400, 425, 450, 475, 500, 525, 550, 573, 575, 600, 625, 650, or675 percent greater.

In a specific implementation, the bottom surface of the sensor unit maybe approximately 107.6 square millimeters and the bottom surface of thecushioning layer may be approximately 616.3 square millimeters. In aspecific implementation, the cushioning layer is at least about 3.2millimeters thick, 21.3 millimeters wide, and 38 millimeters long.

In an implementation, the cushioning layer is flexible. The flexibilityallows the cushioning layer to conform to the shape of the sensor unitand the patient's skin. The result is that the sensor unit is shieldedfrom ambient light. Source light is also prevented from escaping. Thesensor unit uses light transmitted by an optical wave guide, such as afiber optic cable, to obtain sensitive measurements. If light from thesensor unit escapes through the sensor housing, the sensor unit may notdetect this light. Likewise, ambient light entering the sensor housingwill also result in inaccurate readings. When the cushioning layerconforms it creates a dark environment within the sensor housing thatenables accurate readings. The cushioning layer's flexibility is afunction of its size and material type.

The implementation shown in FIG. 5 depicts a cavity in the cushioninglayer. The cable enters the bottom edge of the cushioning layer throughthis cavity. The presence of the cavity provides additional flexibilityto the cushioning layer.

The sensor unit is embedded in a cavity in the cushioning layer. Thisarrangement helps to maintain contact between the sensor unit's bottomsurface and the skin of the patient. The sensor unit is generallyembedded at or near a midpoint 530 of the cushioning layer. In thislocation, the cushioning and light-shielding layers surround the sensorunit to shield ambient light and contain the source light. However, inother implementations the sensor unit is embedded in other locationswithin the cushioning layer. In most embodiments it will not touch anoutside edge of the cushioning layer. The portion of the cable that iscoupled to the sensor unit is also embedded in the cushioning layer.

In a specific embodiment, the sensor unit is a part of the ODISsey™Tissue Oximeter available commercially from ViOptix, Inc. of Fremont,Calif. ODISsey is a trademark of ViOptix.

A specific implementation may also include one or more light-shieldinglayers. For example, there may be one, two, three, or more than threelight-shielding layers. In another implementation, the light-shieldinglayers may be omitted.

In an implementation, the light-shielding layers have the shape of apolygon. They are constructed of polypropylene film metalized withaluminum on the bottom side and coated with a pressure sensitiveadhesive. In other implementations, the layers are made of a foil, amirror, or made of other materials such as gold, titanium dioxide, or acomposite of materials to block or reflect light. Other examples includea light-reflective tape, a material coated with light-shielding paint, amaterial impregnated with light-reflective material, or alight-reflective fabric. The sensor unit itself may be covered or madewith a light-reflective material.

In an implementation, the first light-shielding layer has a shape thatmatches the top surface of the cushioning layer. That is, the firstlight-shielding layer has cavities that correspond to the cavities inthe cushioning layer.

The second light-shielding layer has an opening that overlaps the sensorunit cavity in the cushioning layer. In an implementation, the secondlight-shielding layer is wider than the cushioning layer. It extendshorizontally in equal portions beyond both sides of the cushioninglayer. The total width of the second light-shielding layer may beapproximately thirty to fifty-six percent greater than the width of thecushioning layer. The light-shielding layer can extend by a smaller orgreater percentage as appropriate for the particular application.

The light-shielding layers serve several purposes. They prevent sourcelight from escaping. They reduce ambient light. Placing the thirdlight-shielding layer over the sensor unit and cable also secures thesensor unit and cable in their respective cavities in the cushioninglayer.

In a specific embodiment, the adhesive film is matte finish, 3 miltransparent polyethylene, coated with a hypoallergenic, pressuresensitive acrylate adhesive. In other embodiments, the film is thickeror thinner, opaque or nontranslucent, or includes an alternativeadhesive material (e.g., latex or silicone-based). The adhesive film maybe a coating. The coating may be deposited using a brush or spray. Thecoating may be deposited as a series of small dots or lines. It maycover the entire bottom base of the sensor housing, or it may only covera portion of the bottom base.

FIG. 5 also shows the symmetry of the sensor housing. The cable dividesthe sensor housing into two mirror images. Thus, the sensor housing isequally effective when it is used on either the right or left palms.Manufacturers can minimize their manufacturing costs because they do notneed to manufacture left-handed or right-handed specific sensorhousings.

Several dimensions are also shown in FIG. 5. Many other implementationsare possible. These dimensions may vary considerably depending on thesize of the tissue measured, the size of the sensor unit, or both. Forexample, infants require small sensor housings. In other cases, adultsrequire large sensor housings. Table A below shows severalimplementations for the sensor housing dimensions.

TABLE A First Implementation Second Implementation Variable(millimeters) (millimeters) a1 17.0 16.3-17.8 a2 6.3 6.1-6.6 a3 4.33.6-5.1 a4 22.8 20.3-25.4 a5 8.8 8.6-9.1 a6 21.5 21.3-21.8 a7 34.033.3-34.8 r 19.0 18.3-19.8

FIG. 6 shows a specific implementation of the adhesive film. Here, theadhesive film has a convex shape defined by a peripheral outline 605. Anopening 610 is provided for the sensor unit. Lengths a16 and a15correspond to the width and length, respectively, of the opening. A lineof symmetry 615 divides the adhesive film into two mirror images. Afirst portion 620 is located at the center of the adhesive film. Secondand third portions 625 and 630 of the film extend horizontally from thefirst portion and line of symmetry.

The peripheral outline forms an outer boundary in which the opening isenclosed. All points on a line drawn between any point on the peripheraloutline to any other point on the peripheral outline are enclosed by theouter boundary. Alternatively, the interior angle formed by any threepoints on the peripheral outline is not greater than 180 degrees. Theconvex shape as defined by the peripheral outline is independent of theshape of the opening. There may even be multiple openings. For example,the opening may have a convex or concave shape, the shape of a square,rectangle, circle, oval, triangle, crescent, or multiple combinations ofthese; the peripheral outline will continue to define a convex shape inwhich the outer boundary encloses these openings.

In the implementation shown, the adhesive film is roughly rectangular inshape with curved corners. Second and third portions have a semicircle,convex shape. Second and third portions lie on opposite sides of thefirst portion. Thus, the adhesive film resembles a rectangle withsemicircles attached on opposite sides.

A convex shape has several advantages. For example, a user may be ableto more easily remove the sensor housing from the patient as opposed toan adhesive film having a concave shape. This is because a concave shapehas edges that curve inward resulting in interior angles. As the userpeels away the sensor housing from the patient stress risers are formedat these interior angles. There is then a higher likelihood that theadhesive film will tear at these interior angles. The adhesive film mustthen be made stronger or thicker to resist tearing.

In another embodiment, the adhesive film has concave regions or acombination of concave and convex regions. These regions may be composedof straight line segments, convex line segments, concave line segments,or combinations of these. For example, an appendage such as a tab ormultiple tabs may be attached to the peripheral outline. These tabs mayaid in removal of the sensor housing by providing a place to grasp theadhesive film.

In a specific implementation, the second and third portions each extendapproximately 12.7 millimeters beyond two edges of the secondlight-reflecting layer. In other implementations, these outer portionsmay be smaller or larger. Factors influencing the size of these outerportions include where on the body the user intends to place the sensorhousing and the size of the sensor unit.

The width and length of the opening (i.e., a16 and a15) roughlycorrespond to the width and length of the sensor unit. In a specificimplementation, width a16 may range from about 5 millimeters to about 11millimeters. For example, a16 may be about 7, 7.1, 7.2, 7.3, 8, 8.1,8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9 millimeters long orgreater. Depending on the specific application, the width may be lessthan 5 millimeters, or greater than 11 millimeters.

The length a15 may range from about 7 millimeters to about 13millimeters. For example, a15 may be about 7.0, 7.1, 7.2, 7.3, 7.4, 7.5,7.8, 7.9, 8, 9, 10, 11, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7,12.8, 12.9, or 13 millimeters long or greater. Depending on the specificapplication, the length may be less than 7 millimeters.

In a specific implementation, the area of the adhesive film is greaterthan the area of the opening. The area of the adhesive film may be about14 to 18 times greater than the area of the opening. For example, thearea of the adhesive film may be about 15, 16, 17, or more than 18 timesgreater than the area of the opening. Depending on the specificapplication, the adhesive film may be less than 14 times greater. In animplementation, the adhesive film has a surface area of approximately1836 square millimeters and the opening has an area of approximately 109square millimeters.

The adhesive film allows the sensor housing to adhere to the surface ofthe person, animal, or other living thing being monitored. Thus, it maybe flexible and elastic so that it can conform to the surface. In animplementation, the adhesive film is nonirritating to the human skin. Auser can remove the sensor housing without leaving any residue orcausing any damage to the patient's skin. An adhesive film that islight-transparent, translucent, or semitransparent enables the clinicianto observe the patient's skin color, temperature, and condition throughthe edges of the sensor housing.

In a specific embodiment, the adhesive film may be provided with aseries of perforations. These perforations permit aeration of the skin.The aeration prevents the skin from becoming irritated, especially ifthe sensor housing is attached to the patient for a long period of time.The perforations also impart an additional degree of flexibility to theadhesive film. This too results in increased patient comfort.

In a specific implementation, the adhesive film may also be impregnatedwith antibiotics. This aids in preventing infections to sensitive skin.

FIG. 7 shows a bottom side of a sensor housing 705 and sensor unit 710in accordance with an implementation. A release liner 715 is coupled tothe adhesive film on the bottom side of the sensor housing. A pull-tab720 is attached to the release liner. The pull-tab is positioned at anedge 725 adjacent to a cable 730.

The bottom surface of the sensor unit is exposed. The bottom surfaceextends below the bottom side of the sensor housing in order to contactthe tissue. Sensor openings along axes 735, 740, and 745 face away fromthe top of the sensor housing. Axes 740 and 745 pass through the sourceopenings. Axis 735 passes through the detector openings.

FIG. 7 shows six openings for two sources and four detectors. However, adifferent number of openings are possible. In various specificimplementations the sensor unit may have at least three openings for atleast two source sensors and at least one detector sensor, or at leastone source sensor and at least two detector sensors. There may be, forexample, one, two, three, four, five, six, seven, eight, or more thaneight sensor openings.

Although the sensor openings here are shown on different axes, thesensor openings may all be aligned along the same axis.

In a specific embodiment using fiber optic cables, one fiber optic cableconnects to each opening on the bottom surface of the sensor unit. Forexample, if the bottom surface has six openings, there will be six fiberoptic cables for transmitting optical information between the sensorunit and the monitoring console.

In an embodiment of the invention, each opening and corresponding fiberoptic cable is dedicated to a particular purpose. For example, a firstopening on the sensor unit (and corresponding fiber optic cable) isdedicated to transmitting light from the monitoring console. A secondopening on the sensor unit (and corresponding fiber optic cable) isdedicated to transmitting a signal received at the second opening to themonitoring console.

Some embodiments use a particular opening and fiber optic cable formultiple purposes (e.g., both input and output) using a scheme such asmultiplexing.

In a specific embodiment, a particular opening and cable transmits anoutput to affect a reaction (e.g., sending electrical signals tostimulate muscle or other tissue). Another opening and cable transmitsthe resultant signal back to the monitoring device. In yet anotherembodiment, the openings and cables may simply detect changes andtransmit these changes back to the monitoring device. For example, theopenings and cables may carry voltage changes in the patient's skin backto the monitoring device.

In an implementation, the sensor unit is passive. For example, it willnot contain electrical circuitry or electrical devices, such as a powersource, an amplifier, or photodiodes. A passive sensor unit may haveopenings, each opening holding an end of fiber optic cable. However, inother implementations, the sensor unit is active. It may, for example,contain an amplifier to amplify the signals in the sensor unit. In aspecific embodiment, the sensor unit may contain photodiodes, includingfour photodiodes.

In one embodiment, the cable enters an edge of the sensor housingnearest the openings for the sources. In another embodiment, the cableenters an edge of the sensor housing nearest the openings for thedetectors. In yet another embodiment, the cable enters an edge of thesensor housing mid-way, or part-way between the sources and detectors.Alternatively, the cable may enter from the top of the sensor housing.

The user removes the release liner to expose the adhesive film prior toadhering the sensor housing on the patient's skin. The release liner, ina specific embodiment, is a silicone treated, polyethylene coated,bleached kraft paper. In other embodiments, the liner is made ofmaterials such as claycoated paper, polycoated paper, polyester, orpolypropylene, amongst others. It is treated with a material such assilicone to allow for easy removal from the adhesive film.

In a specific embodiment, the release liner is a single piece with apull-tab to allow removal of the liner from the adhesive film in onepiece. In this embodiment, the pull-tab is generally at the edge of therelease liner closest to the cable. However, the pull-tab can be onother edges of the release liner. In another specific embodiment, therelease liner is in multiple sections. For example, the release linermay be trisected to allow removal of the release liner in stages. Otherembodiments could include fewer or more sections of liner, with orwithout pull-tabs. In lieu of or in addition to a pull-tab, the linermay be split to aid in removal of the liner from the adhesive film.

FIG. 8 shows a sensor unit which is arranged to include a pair ofsources or, more specifically, source arrangements and four detectorsor, more specifically, detector arrangements, in accordance with anembodiment of the present invention.

A sensor unit 803 includes four detectors 806 a-d and two sources 809 aand 809 b. Each source and detector has a reference point. The referencepoints may be the centers of the sources and detectors if, for example,the sources and detectors have circular shapes. Alternatively, thereference point may be defined as some other point, so long as thedefinition is consistent among the sources and detectors. A line 812that is parallel to an x-axis 815 a passes through a reference point foreach detector.

Line 818 is parallel to x-axis 815 a. Line 818 passes through areference point of source 809 a. Line 821 is parallel to x-axis 815 aand passes through a reference point of source 809 b.

In the described embodiment, a distance y1 along a y-axis 815 b betweenline 812 and line 818 is different from a distance y2 along y-axis 815 bbetween line 812 and line 821. It should be appreciated that distance y1and distance y2 may vary widely depending upon any number of factors.The factors include, but are not limited to, the number of sources anddetectors, the overall size of sources 809 a, 809 b and detectors 806a-d, the overall size of sensor unit 803, and the application for whichsensor unit 803 is intended. While distance y2 is shown as being greaterthan distance y1, distance y1 may instead be greater than distance y2.In general, the difference between distance y2 and distance y1 is atleast approximately 0.3 millimeters. For example, distance y2 anddistance y1 may differ by approximately 0.5 or 1.0 millimeters.

The positioning of sources 809 a, 809 b and detectors 806 a-d may varywidely. By way of example, sources 809 a, 809 b and detectors 806 a-dare each approximately one millimeter in diameter. Sources 809 a and 809b are directly below detectors 806 a and 806 d, respectively. In thisexample, sources 809 a, 809 b may be separated by a distance that isapproximately 5 millimeters along the x-axis 815 a, and by a distance y4that is approximately 0.5 millimeters along the y-axis 815 b, asmeasured from the reference point of each source. Detectors 806 a-d mayeach be separated by approximately 1.7 millimeters along the x-axis, asmeasured from the reference point of each detector.

Table B below shows measurements for several implementations. Many otherimplementations are possible as explained above. In a firstimplementation, y1 is equal to d2.

TABLE B First Implementation Second Implementation Variable(millimeters) (millimeters) y1 5 4.0-5.9 y2 5.5 5.0-6.5 y3 1.5 1.0-2.0y4 0.5 0.3-1.5 y5 12.4 12.0-13.0 d1 1.7 1.6-2.4 d2 5 4.2-5.9 d3 8.68.4-9.0

Sensor unit 803 is shown with a width of approximately 8.64 millimetersalong x-axis 815 a and a height of approximately 12.45 millimeters alongy-axis 815 b when detectors 806 a-d and sources 809 a, 809 b are spacedas described in the first implementation above. However, sensor unit 803generally has dimensions that may vary widely, e.g., dimensions whichmay vary depending upon the application for which sensor unit 803 isintended.

While a lack of symmetry in the positioning of sensors relative todetectors has been described as being such that distances betweensensors and detectors are different relative to a y-axis, a lack ofsymmetry may instead or additionally have a lack of symmetry relative toan x-axis.

In a specific implementation, the source and detector structurescomprise optical fiber. For example, one or more radiation sources maybe located in the console. The optical fiber may then transmit the lightfrom the console and through the source structures. The light, afterhaving been transmitted through the patient's tissue, may then bereceived by the detector structures which transmit the received signal(i.e., light) back to photodetectors at the console.

In another implementation, the radiation sources, photodetectors, orboth may be located at the sensor unit. For example, the sourcestructures may include light-emitting diodes (LEDs) and the detectorstructures may include photodiodes.

In yet another implementation, the radiation sources may be located atthe console, while the photodetectors are located at the sensor unit. Instill another implementation, the radiation sources may be located atthe sensor unit, while the photodetectors are located at the console.

Referring next to FIG. 9, a sensor unit that includes a pair of sourceswhich are in an offset (or asymmetrical) arrangement relative to a setof four detectors with respect to an x-axis is described. A sensor unit905 includes four detectors 910 a-d, although the number of detectors910 a-d may vary. Detectors 910 a-d are arranged such that a line 915 issubstantially parallel to an x-axis 920 a and passes through a referencepoint of each detector 910 a-d. A first detector 910 a and a lastdetector 910 d, i.e., the detectors which are farthest apart relative tox-axis 920 a, are used to define a central bisecting line 925 ofdetectors 910 a-d. Central bisecting line 925 is parallel to a y-axis920 b, and is arranged such that a distance x3 from a reference point ofdetector 910 a to central bisecting line 925 is substantially equal to adistance x4 from a reference point of detector 910 d to centralbisecting line 925. That is, central bisecting line 925 is arranged topass through a central midpoint between detector 910 a and detector 910d such that central bisecting line 925 is substantially perpendicular toline 915.

As shown, a reference point of first source 930 a and a reference pointof first detector 910 a are aligned along a line 935 that issubstantially parallel to a y-axis 920 b. Similarly, a reference pointof a second source 930 b and a reference point of last detector 910 dare aligned along lines 940 and 945, respectively, that aresubstantially parallel to y-axis 920 b. It should be appreciated,however, that line 935 may not necessarily pass through the referencepoint of first detector 910 a, and line 940 may not necessarily passthrough the reference point of last detector 910 d. That is, line 935 iseffectively a line that is substantially parallel to y-axis 920 b andpasses through first source 930 a, while line 940 is effectively a linethat is substantially parallel to y-axis 920 b and passes through secondsource 930 b.

A distance x1 between line 935 and central bisecting line 925 isdifferent from a distance x2 between line 940 and central bisecting line925. In other words, first source 930 a and second source 930 b are notequidistant from central bisecting line 925. Hence, sources 930 a, 930 bare positioned in an offset or unbalanced orientation relative to x-axis920 a.

In yet another embodiment, the detectors may not be aligned on the sameaxis. For example, there may be rows of detectors where each row has apair of detectors. The rows of detectors may be separated by a distanceof approximately 10 millimeters. A pair of detectors in a row may beseparated by a distance of approximately 5 millimeters. The distancefrom the sources to detectors may then vary between approximately 30millimeters to 40 millimeters.

Although FIGS. 7, 8, and 9 show sources and detectors havingcircular-cross sections, in other implementations the cross sectionshave a different shape. These shapes may include convex and nonconvexshapes (e.g., a crescent shape), polygons such as a square, rectangle,or triangle, and combinations of these.

Each of the foregoing source and detector arrangements of the presentinvention may incorporate the source and detector arrangements discussedin U.S. Pat. No. 7,355,688, which is incorporated by reference.

Further in other implementations of the invention, the sensor unit hassensor openings arranged in a symmetrical or balanced arrangement. Forone example of a symmetrical arrangement of sensor openings, the sensoropenings are positioned at the corners of a rectangle, square, or otherpolygon where opposite sides have the same length.

In another example, the sensor openings are arranged so there is a firstdistance between a first detector and a first source and a seconddistance between the first detector and a second source, where the firstand second distances are equal. In another example, the sensor openingsare arranged so there is a first distance between a first source and afirst detector and a second distance between the first source and asecond detector, where the first and second distances are equal.

In another example, the sensor openings are arranged so there is a firstdistance between a first source and a first detector. There is a seconddistance between the first source and a second detector. There is athird distance between a second source and the first detector. There isa fourth distance between the second source and the second detector. Thearrangement is symmetrical when the first distance is equal to thefourth distance, and the second distance is equal to the third distance.

FIGS. 10-14 show cross-sectional views of the sensor housing inaccordance with several embodiments of the present invention. The layersshown are not drawn to scale to allow easier visual differentiation ofthe layers within the figure's representation.

In FIG. 10, a stiffener bar 1005 is above a third light-shielding layer1008 and cavity 1011. A cushioning layer 1014 is between a firstlight-shielding layer 1017 and a second light-shielding layer 1020. Anadhesive film 1023 is coupled to the second light-shielding layer. Theadhesive film is covered by a release liner 1026 which has a pull-tab1030. The release liner is on a bottom side of the sensor housing. In analternative implementation, the stiffener bar is embedded in thecushioning layer below the second light-shielding layer, but above thecable. In other implementations, the stiffener bar is absent, or thesecond light-shielding layer is absent, or both the stiffener bar andthe second light-shielding layer are absent.

The cushioning layer contains a cavity 1033. Cavity 1033 is locatedbetween an end of the cushioning layer 1036 a and an opposite end of thecushioning layer 1036 b. The cavity may be a slot, recess, hole, hollowarea, divot, pocket, chamber, or other space. In a specific embodiment,the cavity may be partially enclosed by the cushioning layer. Forexample, the cavity may be enclosed by three portions of the cushioninglayer. In another embodiment, the cavity may be completely enclosed bythe cushioning layer.

Cavity 1033 conforms to the shape of sensor unit 1039. An edge of thesensor unit is generally midway between the ends of the cushioninglayer, though it may be offset from the mid-point in an implementation.

The sensor unit is held in cavity 1033 with an adhesive. The bottomsurface of the sensor is exposed through the cavity, the secondlight-shielding layer, and the adhesive film. In a specificimplementation, the bottom surface of the sensor is also exposed throughthe release liner. The bottom surface of the sensor unit may protrudepast the bottom of the sensor housing from about 0.8 millimeters toabout 2 millimeters. For example, the bottom surface of the sensor unitmay protrude about 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or1.9 millimeters or greater.

Exposing the bottom surface of the sensor unit past the bottom surfaceof the sensor housing ensures that the sensor unit properly contacts thetissue to be monitored. It also allows preliminary measurements of theproposed site before the sensor housing is attached to the patient. Inanother implementation, the bottom surface of the sensor unit is coveredby the release liner. This protects the sensor unit from debris.

Cavity 1011 in the cushioning layer is coupled to cavity 1033. Cavity1011 is intended for a cable 1012. The cavity may be a slot, recess,hole, hollow area, divot, pocket, or other space partially enclosed bythe cushioning layer. This particular figure shows cavity 1011 betweenthe top and bottom surfaces of cavity 1033. In an implementation, cavity1011 has a greater volume than cavity 1033. In other implementations,the volume of cavity 1011 is less than the volume of cavity 1033. In aspecific implementation, the cavities have the same width.

The cable enters through an edge of the cushioning layer and into cavity1011. The cable enters the cushioning layer at an end 1036 a above therelease liner, the adhesive film, and the second light-reflecting layer.The cable connects to the sensor unit at the bottom edge of the sensorunit, at the top edge of the sensor unit, or between the bottom and topedge of the sensor unit.

FIG. 10 also shows dimension y10 which is the overall thickness of animplementation. In the specific implementation y10 is about 4millimeters. However, the thickness may vary. It may be from about 3millimeters to 15 millimeters or greater. For example, the thickness maybe 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 millimeters long, orgreater. Factors influencing the thickness include the presence orabsence of certain items from various embodiments. For example, in anembodiment where the stiffener bar is absent or embedded in thecushioning layer the thickness will be smaller. In another embodiment, adifferent sensor unit may be used that contains, for example,photodetectors or other electronic circuitry to obtain measurementsthrough deeper structures. In that embodiment, the overall thickness ofthe implementation will be greater.

A ratio of the sensor housing's thickness to its overall length, i.e.,aspect ratio, ranges from about 0.03 to about 0.20. For example, theaspect ratio may be about 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2,0.3, 0.4, or greater than 0.4, or less than 0.03. In a specificimplementation, the sensor housing has a thickness of about 4millimeters and an overall length of about 59.4 millimeters. The overalllength is the longest distance between two opposite points on the sensorhousing. This yields an aspect ratio of about 0.07.

Thinner implementations benefit from being less obtrusive. There is lesslikelihood that the device will be accidently jarred causing inaccurateresults. The patient also feels less of a “tugging” sensation. This isbecause the device sits closer to the patient's skin which lessens theamount of torque on the device due to gravity.

FIGS. 11 to 14 show cross-sectional views of several differentimplementations of the cavity for the sensor unit and the cavity for thecable.

FIG. 11 shows depths of cavities 1105 and 1110 having the same thicknessas the cushioning layer. Thus, when viewing the cushioning layer fromthe top, the cavities appear as a slot. The cavity is bounded on threesides by the cushioning layer. In other implementations, the cavitiesmay be fully surrounded by the cushioning layer. Light-shielding layer1115 has an adhesive and covers the cushioning layer, sensor unit, andcable. The adhesive secures the sensor unit and cable in their cavities.

In FIG. 12, cavities 1205 and 1210 have the same depth, but the depth isless than the thickness of the cushioning layer. In FIG. 13, the topsurface of cavity 1310 is on the same plane as the top surface of cavity1305. The figure also shows cavity 1305 having a greater depth thancavity 1310. In FIG. 14, the bottom surface of cavity 1410 is on thesame plane as the bottom surface of cavity 1405. The figure also showscavity 1405 having a greater depth than cavity 1410.

FIG. 15 shows a sensor housing 1505 on a patient's thenar eminence 1508.Cable 1511 is positioned along axis 1514 which is located on a patient'sopen palm 1517. The axis runs through the thenar eminence and a thumb1520. In this particular implementation, the adhesive film includes athree-section release liner, including first (or center), second, andthird portions 1523, 1526, and 1529, respectively. Pull-tab 1532 isattached to the first portion of the release-liner.

Measuring tissue oxygen saturation at the thenar eminence providesseveral benefits. First, the measurement may be used to predict thedevelopment of organ dysfunction during traumatic shock. For example, astraumatic shock begins, peripheral vasoconstriction directs blood awayfrom the limb muscles into the brain. This causes a drop in peripheralmuscle tissue oxygen saturation. Medical personnel may then intervenewith resuscitation efforts. Second, measurement may be used to determinewhen resuscitation is successful. For example, as the shock ends, bloodto the internal organs is restored first, followed by blood to themuscles.

Typically, when using near-infrared spectroscopy to measure tissueoxygen saturation at the thenar eminence, the near-infrared radiation iscalibrated to penetrate the tissue at a depth of approximately fivemillimeters. However, the depth may vary depending if a measurement istaken at a different location. For example, if the tissue to be measuredis below structures such as bone or layers of adipose tissue, then thenear-infrared radiation may be calibrated to penetrate deeper such as 6,7, 8, 9, 10, 11, 12, 13, 14, 15, or more than 15 millimeters.

FIG. 16 shows process flow 1605 which is an application of the sensorhousing in accordance with an embodiment of the present invention. Nothreshold readings are required prior to taking a measurement. In aspecific application, the user monitors the tissue oxygenationsaturation of the thenar eminence, which may assist medical personnel inmonitoring shock-associated hypoperfusion.

In a step 1610, the user removes the sensor housing, and sensor unitwith its attached cable, from the packaging. The cable is generallyflexible. Thus, the user can arrange the cable so it creates a straightline near its entry to the sensor housing.

In a step 1615, the user either removes the entire release liner (a step1620) if it is a single-piece liner or just the first (or center)release liner (a step 1625) if it is a multipiece release liner. Theuser removes the release liner by grasping the cable with one hand andpulling on the pull-tab with the other hand. This exposes the adhesive.The user then adheres the sensor housing to the patient.

In a step 1630, the user locates the axis running from the patient'sthenar eminence through the thumb. Next, in a step 1635, the user alignsthe sensor housing along that axis. In an implementation, figures andtext on the sensor housing, or cable, or both instruct the user on howto properly position the sensor housing. For example, an arrow may bepainted in the middle of the sensor housing. Printed instructions maydirect the user to point the arrow towards the base of the patient'sthumb.

In an alternative implementation, the user may also use the cable as asight. For example, the user first finds the axis along the thenareminence by sighting from the patient's open palm and through the thenareminence and thumb. The user can use the cable, since it resembles anaxis itself, as sight to align the sensor unit over the thenar eminence.In other embodiments measuring the oxygen saturation of other tissues,the user similarly positions the cable so that it runs generally alongan axis of the tissue.

In a step 1640, the release liner is either a single-piece or amultipiece release liner. If the release liner is a single-piece linerthen the user presses the entire sensor housing onto the skin of thethenar eminence, a step 1645. If, however, the release liner is amultipiece release liner, for example, a three-piece release liner, thenthe user presses the first portion of the sensor housing onto the skinof the thenar eminence, a step 1650. In a step 1655, the user removes asecond release liner. The user then presses the second portion of thesensor housing onto the skin to conform the sensor housing to thepatient's body. The user repeats this process in a step 1660 with thethird portion of the sensor housing.

Finally, in a step 1665, the user attaches the cable to the monitoringconsole. The user may disconnect the cable from the monitoring consoleand reconnect it to the same or a different monitoring console withoutcalibration. Alternatively, the user may attach the cable to themonitoring console as a preliminary step. This allows a preliminarymeasurement of the proposed site before affixing the sensor housing tothe tissue.

FIG. 17 shows an alternative implementation where the user attaches asensor unit 1701 without the sensor housing. In this implementation, thesensor unit is not embedded within the sensor housing. Instead, it isleft exposed on all sides. Using the sensor unit without the sensorhousing may be more appropriate in certain trauma situations where useof the sensor housing is contraindicated. Separate material, not coupledto the sensor unit, is used to create a sensor housing to secure thesensor unit. In this example, a finger glove 1705 secures the sensorunit on a patient's fingertip 1710. A ring 1715 on the finger glove iscut to reduce constriction. Cable 1718 runs along a patient's forearm1720. The cable attaches to the forearm with a strap 1725. Ties 1730provide additional strain-relief for the cable.

In an implementation, the finger glove is a latex finger cot. In otherimplementations, the finger glove is made of nitrile rubber, vinyl,cloth, or other flexible materials. In an implementation, the fingerglove has an inner diameter in the range of 18-22 millimeters. It shouldalso be appreciated that instead of a finger glove, other types offasteners such as tapes, bands, belts, or adhesives on the sensor unititself may secure the sensor unit.

FIG. 18 shows process flow 1805 for using the sensor unit without thesensor housing. In a step 1810, the user places the sensor unit aloneagainst the tip of the patient's finger. The sensor unit is positionedso that the sensor openings contact the patient's skin. In a step 1815,the user covers the sensor unit with the finger glove. The finger glovesecures the sensor unit against the patient's fingertip. The fingerglove should cover the fingertip and the sensor unit but should not betoo constricting. In a specific embodiment, the finger glove only coversthe portion of the patient's finger that includes the sensor unit. Inother embodiments, the finger glove covers the sensor unit and a portionof the finger past the sensor unit toward the palm.

In a step 1820, the user makes a vertical cut in the ring of the fingerglove to reduce blood constriction.

In a step 1825, the user stabilizes the sensor unit's position byfastening the cable to the patient's forearm. In an implementation, theuser couples the cable to itself using plastic cable ties. The user thenattaches the cable to the patient's forearm using a loose band ofmaterial that is easy to remove and does not constrict the skin. Thisincludes, for example, a fabric hook-and-loop fastener, self-stickinggauze, tape, belts, rubber bands, plastic-coated ties, and otherfasteners. In other implementations, the cable may not be coupled toitself before it is attached to the forearm. Users may also clip thecable to the patient's clothing, gown, or bedding.

FIG. 19 shows a process 1905 of making the invention. In a step 1910,the manufacturer procures the parts. In a particular embodiment, thisincludes: the adhesive film (with the release liners), the first, secondand third light-shielding layers, the cushioning layer, the stiffenerbar, the sensor unit, and the cable.

In a step 1915, the first and second light-shielding layers are coupledto the top and bottom surfaces of the cushioning layer. The firstlight-shielding layer is coupled such that its cavities overlap thecavities in the cushioning layer. The second light-shielding layer iscoupled such that its opening overlaps the cavity in the cushioninglayer for the sensor unit.

In a step 1920, the adhesive film is coupled to the secondlight-shielding layer. The adhesive film forms the base of the sensorhousing.

In a step 1925, the third light-shielding layer is partially coupled tothe top of the sensor housing. The third light-shielding layer has amultisection release liner. This release liner covers an adhesive on thelight-shielding layer. A first portion of the release liner is removed,exposing an adhesive. A first portion of the light-shielding layer isthen coupled to the top of the sensor housing. The third light-shieldinglayer is coupled such that the first portion does not overlap thecavities in the cushioning layer.

This results in an unfastened flap of the third light-shielding layer.Leaving a portion of the third light-shielding layer unfastened allowsassembly of the sensor housing independent of the sensor unit. If thereis a delay in sourcing parts for the sensor unit, the delay will haveminimal impact on assembling the sensor housing. The sensor housing mayalso be shipped to a different location for installation of the sensorunit. Less protective packing material is needed; the sensor housingdoes not yet contain any fragile parts such as the sensor unit andcable. The shipping weight is also less than it would be if the sensorunit and cable were installed.

In a step 1930, the sensor housing is attached to the sensor unit. Thesensor unit and cable are placed in their respective cavities in thecushioning layer. The sensor unit is positioned to protrude past thebottom surface of the sensor housing. This ensures that the sensor unitcontacts the patient's skin.

In a step 1935, a second portion of the release liner for the thirdlight-shielding layer is removed. The adhesive is now exposed. Theunsecured flap of the third light-shielding layer is then pressed overthe cavities which contain the sensor unit and cable.

Finally, in a step 1940, the stiffener bar is placed above the cavitycontaining the cable.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

The invention claimed is:
 1. A device comprising: a pad region having acavity, wherein the cavity comprises a cavity opening, and the cavityextends from the cavity opening to an inside surface that is opposite ofthe cavity opening, the cavity is positioned between a first end of thepad region and a second end of the pad region, opposite the first end,and a bottom surface area of the pad region is greater than a bottomsurface area of the cavity opening; a first light-shielding layer,coupled to the pad region, wherein the first light-shielding layer hasan opening that overlaps with at least a portion of the cavity opening;and an adhesive layer, coupled to the first light-shielding layer,wherein the adhesive layer extends past at least one edge of the firstlight-shielding layer.
 2. The device of claim 1 comprising: a sensorunit positioned in the cavity; and a cable coupled to the sensor unit,wherein the cable is arranged to enter the cavity, the cable beingarranged to define a longitudinal axis that passes through the cable andthe device, dividing the device into a first side and a second side,wherein the first and second sides are mirror images of each other. 3.The device of claim 2 wherein the cable has a length greater than 1.2meters.
 4. The device of claim 2 wherein the sensor unit comprises: afirst source structure; a second source structure; a first detectorstructure comprising optical fiber; and a second detector structurecomprising optical fiber, wherein a first distance is between the firstsource structure and the first detector structure, a second distance isbetween the first source structure and the second detector structure, athird distance is between the second source structure and the firstdetector structure, a fourth distance is between the second sourcestructure and the second detector structure, the first distance is notequal to the second, third, and fourth distances, the second distance isnot equal to the third and fourth distances, and the third distance isnot equal to the fourth distance.
 5. The device of claim 2 wherein thesensor unit is bounded on three sides by the pad region.
 6. The deviceof claim 2 wherein a tissue-facing surface of the sensor unit is exposedthrough the cavity of the pad region.
 7. The device of claim 2 wherein atissue-facing surface of the sensor unit protrudes from the cavity pasta bottom surface of the pad region.
 8. The device of claim 7 wherein thetissue-facing surface of the sensor unit protrudes a distance from about0.8 millimeters to about 2 millimeters past the bottom surface of thepad region.
 9. The device of claim 1 wherein a bottom surface area ofthe pad region is greater than a bottom surface area of a sensor unitrecessed into the cavity.
 10. The device of claim 1 wherein the padregion, first light-shielding layer, and adhesive layer each comprise atleast two opposing straight edges which are parallel, the pad region,first light-shielding layer, and adhesive layer being arranged so thatthe at least two opposing straight edges of the pad region, firstlight-shielding layer, and adhesive layer overlap, the adhesive layerfurther comprising: a left portion having a shape of a semicircle; amiddle portion having a shape of a polygon; and a right portion having ashape of a semicircle, wherein the middle portion is between the leftportion and the right portion.
 11. The device of claim 1 wherein thethickness of the pad region when uncompressed is thicker than a sensorunit.
 12. The device of claim 1 wherein a stiffener bar is coupled to atop surface of the pad region, above at least a portion of the cavity.13. The device of claim 1 further comprising a release liner, coupled tothe adhesive layer, wherein the release liner comprises a tab positionedalong an edge where a cable enters the pad region.
 14. The device ofclaim 1 wherein the adhesive layer is transparent.
 15. The device ofclaim 1 further comprising a second light-shielding layer coupled to atop surface of the pad region, wherein the second light-shielding layerhas an opening that overlaps with at least a portion of the cavity. 16.The device of claim 1 wherein a ratio of a thickness of the pad regionto a length of the adhesive layer is less than 0.1.
 17. The device ofclaim 1 wherein the pad region has a thickness at least about 3.2millimeters.
 18. The device of claim 1 wherein an edge of the cavityoverlaps with an edge of the pad region.
 19. The device of claim 1further comprising a third light-shielding layer, wherein the thirdlight-shielding layer comprises a coupled portion and an uncoupledportion, wherein the coupled portion is coupled to the device and doesnot overlap the cavity, and the uncoupled portion overlaps the cavity.20. The device of claim 1 further comprising a second light-shieldinglayer coupled to a bottom surface of the pad region, wherein the secondlight-shielding layer has an opening that overlaps with at least aportion of the cavity.
 21. The device of claim 1 wherein the bottomsurface area of the pad region is about 200 to 700 percent greater thanthe bottom surface area of the cavity.
 22. A device comprising: a padregion having a cavity, wherein the cavity comprises a cavity openingand an inside surface of the cavity, opposite to the opening; a firstlight-shielding layer, coupled to the pad region; an adhesive layer,coupled to the first light-shielding layer, wherein a peripheral outlineforms an outer boundary of the adhesive layer, and all points on a linedrawn between any point on the peripheral outline to any other point onthe peripheral outline are enclosed by the outer boundary; and a sensorunit positioned in the cavity, wherein a back of the sensor unit facesthe inside surface of the cavity, and at least a portion of the sensorunit is embedded in the pad region, holding the sensor unit therein. 23.The device of claim 22 wherein the adhesive layer comprises: a firstconvex edge; a second convex edge; a first straight edge; and a secondstraight edge, wherein the first straight edge is parallel to the secondstraight edge, the first and second straight edges are between the firstand second convex edges, the first convex edge is a mirror image of thesecond convex edge, and a cable, coupled to the sensor unit, crosses oneof the first straight edge or second straight edge.
 24. The device ofclaim 23 wherein the cable is transverse to one of the first straightedge or second straight edge.
 25. The device of claim 23 wherein thecable crosses the one of the first straight edge or second straight edgeat an angle other than 90 degrees.
 26. The device of claim 22comprising: a cable coupled to the sensor unit, wherein the cable has alength greater than 1.2 meters.
 27. The device of claim 22 wherein theadhesive layer is transparent.
 28. The device of claim 22 comprising acable, coupled to the sensor unit, wherein a portion of the cable issurrounded by the pad region.
 29. A device comprising: a sensor unit,wherein the sensor unit comprises a first source structure, a secondsource structure, a first detector structure, and a second detectorstructure on a scanning surface of the sensor unit, and a back surfaceof the sensor unit is opposite of the scanning surface; a cable coupledto the sensor unit; and a sensor pad, coupled to the sensor unit,wherein the sensor pad comprises a recessed region that holds the sensorunit, the recessed region has an opening and an inside surface oppositeto the opening, and the back surface of the sensor unit is positionedagainst the inside surface of the recessed region, a light-shieldinglayer, having an opening, is coupled to a tissue-facing surface of thesensor pad and extending beyond a first and second edge of the sensorpad in at least two opposite directions, and the opening overlaps withat least a portion of the sensor unit, and an adhesive layer is coupledto the light-shielding layer and extending beyond a first and secondedge of the light-shielding layer in at least two opposite directions.